Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $214.35   13.835%   $244.0053   $244.01   $244.00   $244.00  
  Purchase #2 $125.54   9.386%   $137.3232   $137.32   $137.30   $137.30  
  Purchase #3 $177.84   13.626%   $202.0725   $202.07   $202.05   $202.10  
  Purchase #4 $75.94   10.663%   $84.0375   $84.04   $84.05   $84.00  
  Purchase #5 $41.90   11.334%   $46.6489   $46.65   $46.65   $46.60  
  Purchase #6 $15.90   9.418%   $17.3975   $17.40   $17.40   $17.40  
  Purchase #7 $218.61   8.526%   $237.2487   $237.25   $237.25   $237.20  
  7 purchase totals = $870.08       $968.7336   $968.74   $968.70   $968.60